The present invention relates to semiconductor laser devices and, in particular, a semiconductor laser device to be used as a light source for optical disks.
Conventionally, there has been provided a semiconductor laser device as shown in FIG. 6. In this semiconductor laser device, as shown in FIG. 6, two leads 23A, 23B out of three leads are attached so that one end thereof passes through a stem body 21 to protrude on a reference surface 21a side. A remaining one lead 23C is attached on a rear surface side (opposite to the reference surface 21a side) of the stem body 21, where the lead 23C and the reference surface 21a are electrically connected to each other. Also, a heat radiation block 22 is disposed on the reference surface 21a side of the stem body 21. A semiconductor laser chip 24 is mounted on a side face of the heat radiation block 22, and an electrode of the semiconductor laser chip 24 is electrically connected to the lead 23A via an Au (gold) line 25. Then, on the reference surface 21a side of the stem body 21, a cap 26 with a window glass 27 attached is fitted to an annular welding portion A near an outer circumference of the reference surface 21a of the stem body 21 by resistance welding, by which the semiconductor laser chip 24 and the Au line 25 are protected and besides the interior of the cap 26 is maintained hermetic. The outer diameter of the reference surface 21a of the stem body 21 is 5.6 mm, and a margin of the outer circumference of the reference surface 21a with the cap 26 fitted is 0.6 mm. The margin of the reference surface 21a near its outer circumference out of the coverage with the cap 26 serves as a reference plane for alignment position of the laser in incorporating this semiconductor laser device into an optical-disk pickup, and is needed when the semiconductor laser device is adjusted in its rotational position.
With the structure of this semiconductor laser device, there are no problems when the reference surface 21a of the stem body 21 is 5.6 mm in diameter. In small-size packages in which the reference surface of the stem body is 3.3 mm in diameter, there is a problem that the internal area of the cap is too small for the formation of the heat radiation block 22 into such a shape that a margin near the outer circumference serving as a reference plane for the alignment position of a laser is ensured outside the cap when the cap is attached, and moreover that the generated heat of the semiconductor laser chip can be sufficiently dissipated. Therefore, broadening the area of the heat radiation block would cause the heat radiation block to come in contact with the inner circumference of the cap, making it inevitable to extend the depth of the heat radiation block (i.e., to provide a tall heat radiation block). However, with such a small-size package, extending the depth of the heat radiation block would make it difficult to fabricate the stem body and the heat radiation block as an integral pressed article, where only the heat radiation block would inevitably be attached later by means of, for example, silver soldering. For this reason, there is a problem that a semiconductor laser device in which the heat radiation block is later attached to the stem body would be high-priced, compared with integrally pressed articles.